We propose to study the role and distribution of osteonectin, the major noncollagenous protein in bone, by analyzing: (1) osteonectin's location during bone mineralization in organ culture (20 day fetal rat calvaria) by immunofluorescence; (2) osteonectin's and bone -carboxyglutamic acid-containing proteins (BGP) role in mineralization in organ culture with antibody neutralization techniques; (3) osteonectin's relationship with other extracellular matrix proteins (ECM) (type 1 collagen, BGP and fibronectin) in organ culture; (4) osteonectin's effect on osteoblast adhesion, morphology and phenotype expression in cell culture (rat osteosarcoma-derived osteoblastic cell line ROS 17/2.8). Additionally we plan to study by radioimmunoassay the modulation of osteoblastic osteonectin production; (5) during bone mineralization in organ culture, and (6) by hormones which influence bone turnover; parathyroid hormone, 1,25(OH) 2D3 and glucocorticoids, and (7) on collagen, fibronectin and osteonectin coated substrates in cell culture. A mineralizing organ culture of fetal rat calvaria which we have developed will be further characterized by quantitating collagen production and by studying collagen organization by polarized light microscopy. Our aim is to determine the distribution and role of ECM components, in particular osteonectin, in relation to osteoblast growth and differentiation in organ culture where the original bone architecture is maintained. Knowledge of the relationship of specific ECM components with each other, their effect on osteoblast phenotype and their modulation by hormones will lead to a better understanding of the function of ECM proteins in bone. Our eventual goal is to learn how to manipulate ECM components to promote normal bone growth and remodeling in vivo for the successful osseointegration of implants, in diseases such as osteoporosis, and traumatic injuries to bone.